Leptodontaceae are defined by the combination of epiphytic habit, branching pattern of clusters of branches alternate with unbranched intervals bearing inflorescences, double sporophytic phenological cycle in which two cohorts of sporophytes mature simultaneously with embryos overwintering, subfoliose pseudoparaphyllia, cucullate calyptrae, sheathing postfertilization perichaetial leaves, central strands lacking in shoots, shortened setae, no annuli, and an exostome that flexes open when moist and flexes inward when dry (hydrocastique), thus serving to disperse spores during wet periods. Leptodontaceae as treated here comprise Alsia, Forsstroemia, and Leptodon. Recently described or relocated genera in the family include Caduciella Enroth, Cryptoleptodon Renauld & Cardot, and Taiwanobryum Noguchi (J. Enroth 1992). Molecular evidence indicates that this small family may not be monophyletic, and is better viewed within the larger context of the family Neckeraceae (S. Maeda et al. 2000; M. S. Ignatov et al. 2006).